What should my IAC Counts at idle be?

[jmgtp]

91/5spd

I have the chip set at a 750 rpm hot engine idle. The iac counts were at about 70 which seems high to me. When the a/c is on it likes to stall the engine when the revs come down and I think its due to the iac not being able to respond quickly enough because it was already at 70 counts to begin.

I ended up adjusting the throttlebody so that when it is idling the iac counts came down to about 40. It still idles around 750 rpm but the tps is now reading ~1.4%

The car has a lot of mods and a 75mm northstar tb. I like the 750 rpm idle (yes I know, the dohc likes a lil more idle speed than that). The TB has a small hole in the plate to let some air in for idle. Would my solution be to enlarge that hole just enough to get the iac counts at around 20 with 0% TPS? What is the ideal hot idle IAC count?

[IsaacHayes]

Put the TB back to where it was. You don't want the TPS reading anything but 0 it will cause problems.

The hole in the TB plate is called something like an air bleed hole or something, but I think the hole is just to let the air come through there instead of wearing away around the edge of the plate. I've had several 3400/3100 TB's and some had the hole some didn't so it's not for letting air in for idle. It's some other reason. Possibly to reduce whistle. Leave the hole alone.

Make sure the IAC/etc is clean and not carbon'ed up. Other than that you'll probably need to just tune the chip to raise the idle. The IAC counts can go pretty high, IIRC upwards of 150 or so.

[1988GTU]

Log the blm's. Anything higher than 128 indicates lean. 128 should be a good number to adjust it too. TPS higher than .46 volts would cause it to think it's not at idle anymore = high AF & high IAC.
I think 70 is a good number for IAC #'s.

[SappySE107]

70 is high. Since you don't have the stock TB, I am going to say adjust it so its closed but not sticking,, and reset the computer so it resets your TPS % (your voltage can be over .5).

[IsaacHayes]

Really? I've tried pulling the power to the ECM several times when I had higher than normal voltage on my TPS and it never worked. In the end I put on a known good TPS... But who knows it might have kept rising. It never got to 100% TPS either. Like 90 something.

[SappySE107]

You did an OBD1 conversion right? Brad did this and had a problem with his TPS using voltage only. Turned out to be a wiring issue on hte 5 volt reference. I really don't know what the specific problem was though.

[IsaacHayes]

Me? No it's stock OBD1."5"

[SappySE107]

I haven't messed with your setup so it may be different. I have had .6 volt at idle on the TPS. It still sounds like a 5 volt reference issue but if its working, who cares:P 90% throttle means the same as 100% really so as long as its linear between you won't have a problem.

[IsaacHayes]

Right I figured the PE wouldn't matter, I just noticed in scanner pro the TPS didn't have full resolution. It kept giving me high idle randomly, so I swapped it out, and I have full resolution. So it might have worked at a higher volt at idle if it was reliable.

[jmgtp]

I'll try this today.

What is the ideal IAC Counts at idle? 20-30 sounds right to me...?

If I adjust the throttle blade to get it in the 20-30 counts at hot idle the TPS will be reading around 2% I think........ hoping the ecm reset will make that value 0 again.

I think if I can get the counts to come down, and therefore give the IAC more positive range, the engine will be able to recover on a clutch in decel with the a/c on and avoid a stall. It doesn't alway stall but it will usually dip too low and the all it takes is a load on the power steering or something else to push it over the edge.

[IsaacHayes]

IIRC 15-30 was normal for me. This was in cooler weather though.

Make sure your charging system is healthy (battery included) and the IAC is not dirty. It could be slow from carbon. I've had those cause my car to dip too low in RPM before. What chip are you running? Stock? You didn't swap to 5spd from an auto trans did you?

[jmgtp]

Car is a stock 5 speed. The chip is one Ben has been tuning. I did change the idle speed to lower than what he had set.

The TB was new when it went on (with new IAC and TPS) and the egr has been off so it shouldn't be carbon.

Alternator seems to charge just fine at 750 rpm - I do have an OVERdrive pulley on the alternator though, so that helps. Battery is a 2yr old red top in the trunk that seems to be just fine (no probs starting etc and I'm running 00 gauge diesel locomotive wire for both power and ground all the way to the front.

[jmgtp]

Ok.... I adjusted the TB plate until the IAC counts were down to about 15 on a hot engine idle. I then reset the ecm and the TPS % did go back to zero (had to pull the batt cable - pulling ecm fuse didnt work to get it to 0).

It seems more stable but I can still get it to stall with the a/c on. Monitoring with TunerPro I can see that the IAC counts go up by about 20 steps when I turn the a/c on. Can a possible solution be to make the IAC counts go up more when the a/c is on? Maybe try 25 to start and then adjust from there? I don't know where this is in the code though. Is it a flag, a table etc?